Arthur e



A. E. HALL.

ELECTROLYTIC PRODUCTION or zmc.

APPUCATON "LED IULY|5|19|5. 1,380,? 1 1 Patented June 7, 1921.

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simple leachin UNITED" STATES PATENT. OFFICE,

amazon E. new, or OMAHA, mnasxa, ASSIGNOR 'ro amnnrcm smm q m imrmme comm, or new YORK, n. Y., a coaronanou or NEW JERSEY,

ELECTROLYTIC PRODUCTION OF ZINC.

To all whom it may concern:

Be it known that I Airmen E. HALL, a citizen of the United States, residin at- Omaha, in-the county of Douglas and btate of Nebraska, have invented certain new and useful Improvements in Electrolytic Production of Zinc, of which the following is a full, clear, and exact description.

My present 'invention relates to the recovery of zinc .in metallic form from oxidized zinc ores, roasted sulfid ores, and articularly zinc oxid fumes, blue powder i150 known as zinc dust), cyanid precipitates, and zinc dresses. Itschief object is to provide an effective and economical process for the purpose. In the preferred mode of procedure the process is continuous and cyclical, and the metal is deposited electrolytically on suitable cathodes or starting plates.

In the accompanying drawing I have shown in plan an apparatus suitable for practising the recess in the preferred manner. Inasmuc as the invention is not limited to any particular apparatus, and since devices suitable for the purpose can readily be provided by any one skilled in the art, it is sufiicient to illustrate the apparatus in a purel diagrammatic way and I have according y done so in the annexed drawing.

In starting the rocess I treat an excess of crude zinc-oxid-bearing material with dilute sulfuric acid, for example in a suitable vessel 7. This treatment may consist in of the crushed material, or the contents 0 the vessel can be a 'itated by any suitable means, not shown. he residue, which for convenience may be termed residue R,, still contains zinc oxid, and is from time to time removed to a vessel 8, for further treatment as described hereinafter; while of thesolution (non-acid because of the excess of zinc oxid in vessel 7) part is delivered to a suitable vessel 9 for purification as described later and the remainder, with the purified solutionfrom vessel 9, is delivered to the storage tank 10. The solution in' the storage tank, which we may for convenience call solution 5,, is thus an aqueous solution of a 'zinc salt, neutral and of suitable concentration, free from iron, copper, arsenic, antimony and other impurities unfavorable to the electrolytic Specification of Letters Patent.

Patented J ine '7', 1921.

deposition of metallic zinc. As the requires the presence of chlorin in this solution it may be necessary to add chlorin thereto in the form of sodium chlorid, or zmcchlond, or both, in amount suflicient to make the chlorin content 0.10% or more.

Solut1on S is conveyed to a series or cascade of two or more electrolytic depositlon cells, as 11, 12, 13, by amanifold 14, and asses from cell to. cell though pipes 15. t is finally delivered from the last cell to a manifold 16. The cells contain the usual anodes and cathodes, as 17, 18, (which may be of lead and aluminum respectively), connectedby taps or leads 19, 20. to the current supply-mains. In the bottom of each cell is a system of perforated pipes, as 21, sup lied with air under pres sure by a manifo d 22 leading from a suitable source not shown, The pipes 21 are arranged to discharge the air uniformly be tween the electrodes of each pair; that is, between each anode and cathode. The agitation thus produced is important, as it preyents or minimizes pocketing and consequent local impoverishment of the electrolyte, and also depolarizes the cathode by causing detachment of any hydrogen: or other bubbles that may form thereon, These process results tend to make the cathode deposits the ele 'trolyte comes iiinhtralfbut the process has been in operation for a time it contains from 0.05% to 0.50% free sulfuric acid liberated by the electrolytic action. This relatively low acidity gives the electrolyte a hi h resistance to the flow of current, and I therefore use a minimum current density. I have found in practice that thirteen amperes per square foot of cathode area is about as low as is consistent with a good deposition of metallic zinc.

In the second cell the electrolyte enters with some free sulfuric acid, and more is produced by the electrol tic action in the second cell. Because of t is greater acidity and consequent less resistance of the liquor to the flow of current the current density in the second cell can be considerably increased,

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anodes or can be used for the purpose de-" i to the amount of chlorid served thatthere is less polarization of the anodes'than is usually encoimtered, and the solution issuing from the cascade (which we will call solution S will be found to contain free chloric acid. Moreover, lead peroxid (or dioxid) is recipitated in the cells. These results can ex lained on the theory that the chlorid pre nt (sodium or zincchlorid, or both, as mentioned above) is oxidized to'chlorate by the anode reactions and that as the solution becomes acidic this chlorate is decomposed, liberating chloric acid; and that this chloric acid attacks the lead anode to a considerable extent, forming lead chlorate, which in turn is decomposed by the anodic reactions into lead peroxid and chloric acid. In thisway the polarization of the anode is eliminated or greatly diminished, a result which contributes markedl to making it possible to use a current densit of thirteen amperes per square foot of cat ode I area in a nearly neutral electrolyte, with a drop-of voltage of only about 3.5 volts acroa the cell.

The lead peroxid produced is of a lflaky nature and sinks rapidly to the bottom of'the cells, whence it is removed in any con'venient manner, as by sluicing it out, after which it can be reduced to metal and cast into scribed hereinafter. It may be said that the cost of reducin the peroxid is much more than ofiset by the saving of current incident to its production. I y

The aforesaid solution 8,, issuing from the last cell, containschloric acid, corresponding resent at the be- This acid in the subs uent leaching operation oxidizes an so uble ferrous i ron to ferric iron, in whic form the iron is precipitated when the solution is used later to treat zincoxid-bearin material in excess as. hereinafter descri When this solution, purified, returns to the storage tank for subsequent electrol sis in the deposition cells it contains all the clllorin, in the form of chlorids, corresponding to the ginning of the cycle.

original. chlorids.

lution S issuing from the last cell, impoverished as to zinc content and enriched as to content of free acid.( articularly sul furic) is delivered in consi erable excess to vessel 8 containing residue R, as previously described. This solution by reason of its hiihgh content of free acid has a high leachin e ciency and hence dissolves ractically a l the zinc oxid in the said resi ue, leavin a residue which we may call residue R he latter is removed to a suitable filter (not shown), washed, and may then be treated in any convenient manner for the recovery of any lead, copper, gold or silver values contained.

The solution produced by the described leaching or other treatment of residue R which we may call solution S contains free acid (because of the excess acid in solution 8,), and, together with the filtrate from the washing of residue R is transferred to vessel 7, where it is used to treat an excess of zinc-oxid-bearing material, as described at the outset. This operation neutralizes the remaining free acid in the solution and precipitates all iron, copper and similar impurities. This solution, at least partially purified, we shall call solution 8,.

In solution S, there may be other impurities, as antimony and arsenic, these being usually or often present in soluble form in thecrude zinc-oxid-bearing material. To

reduce these to a harmless or negligible peramount added to the purifying tank can be increased; in which case the amount of solution S; used is also increased. In this purif ing operation the arsenic and antimony are a l precipitated and the zinc in the blue owoler is converted into sulfate, available or electro-deposition. The addition of the small amount of acidic solution 8,, from the deposition cells, is for the purpose of starting the action. The solution from the purifying tank 9, which we may call solution 8,, and solution S from the leaching tank 7, are transferred to a suitable filter 23 and thence to storage tank 10 as solution S,. This completes t e cycle.

, The foregoing operations, which, it will be understood, are carried on continuously, in? be summarized briefly as follows:

- rom the storage'tanklO solution S is delivered to the cascade of deposition cells 11, 12, 13 and issues therefrom as solution S poor in zinc but relativel richjn free sulfuric and chloric acids olution S, is-conveyed to vessel 8, where it is used in excess to treat the zinc-oxitT-bearing residue R from vessel 7. lssuingsgfrom the latter it still contains free acid and, now termed solution S is delivered to vessel 7 containing an excess of zinc-oxid-bearing material, where the iron and copper are precipitated and all the free acid is neutralized by combination with zinc. Residue R from the dissolving operation in tank 8, is removed from time to time for recovery of lead, copper, gold, silver, etc., and the residue R, from tank 7 is removed to tank 8. From tank 7 a portion of the liquid, now called solution 8,, is delivered throu h filter 23 to storage tank 10 as solution S 5, while the remainder passes to tank 9 where it is boiled with the proper quantity of solution S (from the deposition cells) and a small amount of blue powder to eliminate arsenic and antimony. Issuing from tank 9 as solution 8,, it flows with solution S to filter 23 and thence to tank 10 as part of solution S The residue from the purifying tank 9, which we may call residue R is removed at convenient intervals and treated in any suitable way, as by smelting, etc., to recover any lead or other values contained therein. If blue powder is not available for the purifymg operation, iron, preferably in the form of scrap, is used in the boiling tank 9, thereby precipitating the arsenic and antimony. Any excess iron is then removed and to the solution in the tank is added lead peroxid (derived from the deposition cells as previously described), which completely precipitates any dissolved iron. Inasmuch as only enough iron is dissolved to replace the arsenic and antimony the amount of lead peroxid needed for removal of the iron is small. However, if the peroxid is not continually available in sufiicient amount, the residue from tank 9, in which residue the lead is present as a lower oxid, having given up part of its oxygen to the iron, is converted into red lead, as byheating for a suilicient time (say forty-eight hours) with access of air. The red lead so produced can then be used instead of peroxid to precipitate the iron. Otherwise the lower oxid in the said 1resildue can be readily reduced to metallic The zinc deposited on the aluminum cathodes or starting sheets is stripped off, and is a superior grade of zinc suitable for purposes to which any grade of zinc can be put.

It is to be understood that the invention is not limited to the procedure herein specifically described, but can be ractised in other ways without departure from its spirit.

I claim:

1. The continuous and cyclical recess of producing metallic zinc by electro ytic deposition, comprising delivering to a cascade of deposition cells having lead anodes a neutral solution of a zinc salt, containing chlorin in suitable form; electrolyzing the solution with successively higher current densities, whereby zinc is deposited in metallic form and the acid of the zinc salt liberated, and lead peroxid and chloric acid are produced; removing the lead peroxid from the cells; treating with an excessof acidic solution from the cascade the residue left from previous treatment of an excess of zincbearing material, whereby the zinc of said residue is substantially all dissolved and the solution left acidic; treating with the acidic zinc-bearing solution fresh zinc-bearing ma terial in excess, thereby neutralizing the solution, precipitating iron and similar impurities, and leaving zinc-bearing residue for treatment with an excess of acidic solution from the cascade as described above;

treating more or less of the neutral solution to purification to remove other impurities; and returning the neutral solution, with the purified portion thereof, to the cascade of deposition cells.

2. In a cyclical process of producmg metallic zinc by electrolytic action the steps comprising electrolyzing in a suitable cell having a lead anode a neutral zinc-Salt solution containing chlorin in the form of chlorid, whereby metallic zinc is deposited on the cathode with liberation of the acid with which the zinc was combined, polarization of the anode is decreased, and lead peroxid and chloric acid are produced; removing the lead peroxid; treating crude zinc-bearing solid material with an excess of acidic solution from the cell, whereby zinc is dissolved and any iron dissolved in ferrous form is converted to ferric form by the chloric acid; treating with the still acidic solution an. excess of crude zinc-bearing solid material, whereby the remaining acid is neutralized by combination with zinc and iron is precipitated from the solution; and returning the now neutral solution to the deposition cell.

3. In a cyclical process of producing metallic zinc by electrolytic deposition, the steps comprising electrolyzing a neutral zinc-salt solution, whereby zinc is deposited and the acid with which it wascombined is liberated; treating with the now acidic solution an excess of crude zinc bearing material. whereby the acid is neutralized by combination with zinc in said material; boiling this solution together with a small amount of an acidic solution with blue powder, whereby any arsenic and antimony in solution are replaced by zinc contained in the blue powder and the arsenic and antimony are precipitated; and returning the neutral and now purified solution for electrolysis.

4. In the extraction of zinc from material containing zinc oxid in the wet way, the step of leaching an excess of zinc-oxid-bearing material with a solution containing sulfuric acid and chlorin in a form capable of oxidizing ferrous iron dissolved fromsaid material.

5. In the electrochemical treatment of zinc leachings, the step of passing a solution containing dissolved zinc salts through a series of electrolytic cells in which successively greater current densities are used.

6. In the extraction of zinc from material containing zinc oxid in the wet way, the cyclical operation of leaching zinc-oxidbearin material with a solution containing sulfuric acid and a chlorid, drawing off the solutions thereby produced, and electrolyzing the same to produce a solution containing sulfuric acid, leachin an additional quantity of the zinc-oxldcaring material therewith, and repeating the cycle of operations.

7. A process of obtaining metallic zinc from material containing zinc compounds soluble in acid, which comprises leaching said materials with an acid solution to produce a solution of zinc salts, passing said solution successively through a series of electrolytic cells in which successively greater current densities are employed, treating zinc-oxid-bearing material with the resulting acid liquid, and repeating the cycle of operations. 1

8. The continuous and cyclical process of producing metallic zinc by electrolytic deposition, comprising treating an excess of zinc bearing material with a solution containing a relatively large amount of sulfuric acid and a relatively small amount of chlorid, whereby zinc is dissolved as sulfate, electrolyzing said solution to deposit metallic zinc and to produce a solution containing free sulfuric acid and chloric acid; treatingzinc-bearing material with said solution, and repeating the cycle of operations.

9. The continuous and cyclical process of producing metallic zinc which comprises passing a solution containing zinc salts through electrolytic cells, and electrolyzing it therein, to deposit zinc and to produce a solution containing free acid and an oxidizing agent; treating material relatively poor in zinc with a portion of said solution containing free acid, whereby substantially all the zinc in said material is dissolved, and the solution left acid; treating an excess of material relatively richin zinc with the still acid solution, whereby all the remaining acid of the solution is neutralized by dissolving zinc, and impurities are precipitated, further purifying said solution by treating the same with another portion of the acid solution containing oxidizing agent, adding blue powder to the mixture and boiling the same, and thereafter returning'the so purified solution containing zinc compounds to the electrolytic cells,

10. The herein described cyclical process of treating zinc-oxid-bearing material which comprises subjecting zinc-oxid-bearing material to an excess of an acid leaching solution containing sulfuric acid and a chlorin compound having oxidizing properties, then subjecting an excess of zinc-oxid-bearing material to the resulting solution, removing undissolved materials from p the solution, electrolyzing the solution to produce metallic zinc and to regenerate the acid leaching solution containing a chlorin compound having oxidizing properties and repeating the cycle of operations. 7

11. In the process of leaching zinc bearing material, the step of purifying the solution from arsenic,'antimony and similar materials by heating the same with finely divided metalllc zinc.

12. The step which com rises boiling a solution contalning zinc sul ate and impurities such as arsenic, antimon and the like with finely divided metallic zinc and with a small amount of an acid liquor.

13. The cyclical process of leaching zincoxid-bearing materlal which comprises (1) treating zinc-oxid-bearing material with an excess of an acid solution containin sulfuric acid, (2) separating the liquid rom the undissolve'd residue, (3) treating an excess of zinc-oxid-bearing material with said solution in the presence of an oxidizing agent, whereby iron is precipitated, (4) and separating the liquid from the undissolved residue, (5) electrolyzing the liquid thereby J produced to simultaneously deposit zinc and produce an acid leach liquor containing the oxidizing agent.

14. In the electrolytic production of zinc the step .of electrolyzing a solution of zinc sulfate containing a chlorid'of an alkaliforming metal, whereby zinc is deposited and a solution containing sulfuric acid and a chlorin-containing oxidizing compound reduced, and thereafter treating zinc-oxidearin material with the said solution.

15. n the electro-chemical treatment of leached solutions containing zinc, the step of assing a solution of a zinc salt of an acid whlch salt offers a higher resistance to the flow of electric current than does said acid, through a series of electrolytic cells, in which successively greater current denslties are em loyed.

16. he process which comprises passing through a series of electrolytic cells, a solution of a zinc salt of an acid, which salt oflers higher resistance to the flow of current than does said acid, and employing successively higher current densities in the successive cells. i

17 The herein described step which comprises electrolyzing a solution of a zinc salt while introducing air near the bottom of the solution, whereby the solution is agitated lytie cells, in which successively greater cutand kept substantially uniform throughout rent densities are used. 10 its body as regards concentration and acid- In testimony whereof I hereunto aflix my ity. V signature.

18. As an improvement in the'treatment ARTHUR E. HALL. of leach-solutions containing zinc sulfate, Witnesses: the ste of assing a solution containing F. S. Homoox, zinc su fate t rough a plurality of electro- SIMEON JoNEs. 

